Within the educational system, teachers are being given the responsibility of preparing students for global citizenship in a global society. This study is about global citizenship education in the context of university English classrooms in Korea. Throughout the 2023 spring semester, based on sustainable development goals adopted by the United Nations, the instructor set learning objectives for students in English classroom to prepare them for global citizenship and offered global citizenship related lectures with a focus on sustainable development goals using texts and online content dealing with a variety of issues in the 21st century. A total of 39 university students participated in the study. In addition to the questionnaire which most previous studies focused on, the present study aims to capture English learners’ voice through semi-structured interview as well. The collected data were analyzed quantitatively and qualitatively. It turned out that the students’ overall perceptions and understanding of global citizenship were improved and they showed positive changes in affective factors.